Embodiments of the invention relate to a primer coating for use on polymeric substrates, and more particularly, to a primer coating including an amorphous polyvinyl alcohol and polyethyleneimine which can be applied to substrates which are subsequently supplied with a metallized coating to provide a polymeric substrate having improved gas barrier properties.
Thermoplastic polymer films such as polyamide and polyester films have excellent strength, transparency, and are widely used as packaging materials for food, cosmetics, medicine, and the like. However, such films are relatively permeable to gases such as oxygen. During storage, gases can permeate the film and interact with the package contents, causing degradation thereof.
Gas barrier coatings or primers are known in the art for use on polymeric substrates used in packaging to provide a barrier to prevent degradation of the product. One known gas barrier coating is crystalline polyvinyl alcohol, which exhibits excellent gas barrier properties under low humidity conditions. However, as the humidity increases, the gas barrier properties of the coating decline rapidly.
Another known gas barrier coating is a metallized coating. Such a coating typically comprises a thin layer of aluminum which is applied to a substrate by vacuum deposition. Such a metallized coating reduces the permeability of the polymeric film substrate to light, water and oxygen. However, it would be desirable to improve the adhesion of metallized coatings to the substrate and to improve the gas barrier properties of such coatings.
Accordingly, there is a need in the art for a primer coating for use on polymeric substrates which is receptive to subsequently applied metallized coatings and which enhances the barrier properties of the substrate to which it is applied.